Bibliometric and visualized analysis of scientific publications on subglottic stenosis based on web of science core collection

Background Subglottic Stenosis (SGS), with increasing numbers of studies, is the most specific and common clinical type of Laryngotracheal Stenosis (LTS). There is rapid publication turnover with newer management introduced and expanding research field. To our knowledge, there is no bibliometric analysis of SGS yet. Methods In August 2022, we performed a thorough search in the Web of Science Core Collection database using the word “subglottic stenosis,” and “SGS.” The 580 articles were arranged based on correlation. The collected articles were then analyzed with an assessment of relevant factors. Meanwhile, we analyzed the top 100 most-cited articles on SGS. Results The frequency of publication on SGS has increased substantially over time. The USA has contributed the most articles (n = 301). Vanderbilt University published most of the articles among other institutions (n = 18). Laryngoscope topped the list of journals and has published 89 SGS-related articles. Research hotspots shift from surgical treatment to conservative management. Conclusions The SGS-related literature has grown rapidly in recent years. This study represents the first bibliometric analysis of scientific articles on SGS. Areas to improve in SGS research can be identified after this analysis of the most impactful articles on this topic.


Introduction
Subglottic stenosis (SGS) is a congenital or acquired condition characterized by a narrowing of the upper airway extending from just below the vocal folds to the lower border of the cricoid cartilage [1].Compared with congenital and acquired, idiopathic subglottic stenosis (iSGS) is a relatively new entity [2,3].Idiopathic subglottic stenosis (iSGS), a rare fibrotic disease, is a clinical challenge in terms of etiology, pathogenesis and management [4][5][6].The management strategy of SGS depends heavily on the level by Myer-Cotton grading scale.Mild stenoses (grades 1 and 2) treated non-surgically (therapeutic endoscopy) and severe stenoses (grades 3 and 4) usually require surgical intervention (laryngotrachectomy) [1,7].Studies have demonstrated that therapeutic endoscopy has fewer complications compared to surgery, however, it has a high recurrence rate and requires repeated interventions [8][9][10].Research shows that the extubation rate of T-tube reconstruction after laryngotracheectomy exceeds 95% [11][12][13].
Currently, research on SGS has expanded rapidly, including etiology, pathogenesis, clinical staging and management patterns.Recently, bibliometric analysis has been widely utilized to quantitatively and qualitatively evaluate the publication trends and hotspots of research, including its authors, journals, institutions, and countries [14][15][16].To our knowledge, however, there is no bibliometric analysis of global scientific research on SGS yet.
Here, we performed the first bibliometric study aiming to better understand the research status and publication trends, which may be helpful to determine future direction.Furthermore, we also provide a list of the top 100 most cited articles on SGS between 1968 and 2020.

Search strategy
All data were obtained from the Web of Science Core Collection database.The search was conducted on August 1st, 2022.The search strategy was as follows: Title = (subglottic stenosis OR SGS) AND Document type (article OR review) AND Language = English AND Time span = 1900 to 2022.

Tools
VOSviewer, CiteSpace and Microsoft Excel 2021 were used to analyze the data.The WoS covers a wide range of publications from different fields [17][18][19].VOSviewer and CiteSpace are software tools based on Java which assists with visualization and analysis of bibliometric data.We obtain visualized networks of authors, countries, institutions, co-citation of references, and cooccurrence of keywords.

Data extraction
The procedure for extracting the bibliometric indicators was carried out by two of the researchers (Z.Y.P and D.Z.Q).Each of the observers recorded the information separately.A third observer collated the records of the first two.This is to demonstrate the accuracy of the information extraction process.In cases where there was no consensus, this third observer (X.J.N) verified each of the indicators and made corrections if needed.A general matrix of the studies was then obtained, which made it possible to analyze the bibliometric indicators.Authors, journals, institutions, countries, and total citations were extracted for data analysis.

Publication trend
A total of 580 articles were published by 2042 authors from 547 institutions in 44 countries.These articles were published in 138 journals and cited for 13,718 times.Overall, the number of publications increased dramatically, especially after 2015 (Fig. 1A).

Country distribution
The distribution of the top publication countries is shown in Fig. 1B.Among them, the USA published the largest number of articles (n = 301), followed by the UK (n = 44), Canda (n = 27), and Australia (n = 22) (Fig. 1C).That the USA is the leading country by a wide margin in terms of both impact and volume of output is unsurprising in view of the large population size and leading position of the USA in medical research (Fig. 1D).
In terms of collaborative relationships between institutions examined in our network visualization analysis, Vanderbilt University had the highest total link strength (n = 67), followed by Mayo Clinic (n = 52), Johns Hopkins University (n = 41) and University of Utah (n = 41).In this analysis, the thickness of the line reflects the frequency of co-authorship collaboration among the institutions (Fig. 2C).

Journal of publication
The 580 publications were published in 138 academic journals.The top 10 Journals published 62.6% of all publications (Table 1).The top 3 journals were: Laryngoscope, Annals of otology rhinology and laryngology and International journal of pediatric otorhinolaryngology.Annals of otology rhinology and laryngology had the highest number of citations.The Journals with more than 20 of the publications on SGS, mean impact factor (IF) was 2.991.

Keywords analysis and research interest
Figure 3 shows the co-words network of the most common keywords of the articles published.After setting the minimum number of occurrences of the publication to 10, 54 keywords were obtained.Research areas include susceptible population, classification, management, and outcomes.Figure 3B shows that the keywords change over time, and the color of the keywords varies from year to year.Some keywords frequently appear in each period, such as "subglottic stenosis, " "management, " "tracheal stenosis, " and "laryngotracheal stenosis (Fig. 3C)." In the early days of SGS research, "infants, " "tracheotomy, " "laryngeal stenosis, " "cartilage, " and "anterior cricoid spilt" were the main research hotspots.Notably, "voice, " "balloon dilation, " "idiopathic subglottic stenosis, " and "bronchoscopy, " represented some of the current hotspots.

The 100 most-cited articles
The top 100 most-cited publications on SGS identified in our study were published between 1968 and 2020 (Table 2).The period with most publications was 1981 to 1990 and 2001 to 2010 (n = 22 respectively) (Fig. 4A).A total of 16 countries/regions contributed to publications.A visual analysis of the country distribution shows that countries such as the United States (n = 67), Canada (n = 5), Switzerland (n = 5), and the United Kingdom (n = 4) are the most notable countries for co-authorship publications, and these countries not only have the highest number of publications but also rank highest in centrality (Fig. 4B).University of Cincinnati contributed 6 publications out of the 100, the highest among the institutions represented, followed by University of Pittsburgh (n = 5) (Fig. 4C).
Overall, the 100 most cited publications were published in 25 journals.Annals of Otology Rhinology and Laryngology was the most popular journal with 30 articles and a total of 2586 citations.It was followed by Laryngoscope with 24 articles and 1682 citations.Archives Of Otolaryngology-Head & Neck Surgery contributed 8 articles with 444 citations.Otolaryngology-Head and Neck Surgery, and The Journal of Thoracic and Cardiovascular Surgery both published 5 articles with 444 and 233 citations, respectively (Table 3).
The timeline map of keywords can clearly observe the time span of each cluster and the development trend of a specific cluster, explore the time characteristics of research field reflected by each cluster, and thereby verdict the evolution trend of hotspots.According to the Fig. 5B, the longest lasting heat was "airway stenosis, " starting in 1992 and continuing to 2019.These latest keywords are "hypertrophic scar, " "in-office treatment, " and "keloid." And the shortest duration cluster was "metallic tracheal."

Discussion
For newcomers to a field of study, a bibliometric review can provide an invaluable overview of knowledge in the era of big data, allowing them to conduct research more efficiently.Bibliometric analyses are well-established methods for quantifying quality and scholarly impact and have been widely used to assess the developmental characteristics of a given topic.SGS is the narrowing of the upper airway, which lies between the vocal folds and the lower border of the cricoid cartilage.Studies have shown that up to 12% of all positive cases of infection by novel coronaviruses may require prolonged tracheal intubation for mechanical ventilation or tracheotomy [20].The most common airway-related complication of this operation is laryngotracheal stenosis, with subglottic stenosis being the most common type [20].Meanwhile, in the general environment of COVID-19, based on the pathogenesis of SGS and the increase in the number of people undergoing endotracheal intubation, experts are predicting that there will be a large increase in the incidence of post-intubation (PI) SGS [21].The size of the tracheal tube, duration of intubation, traumatic intubation, presence of infection

Trends in the publication of SGS scientific literature
The United States leads all countries in both total publications and citations, indicating the dominance of the United States in SGS research.In terms of institutional contributions, Harvard University published the most articles with a total of 23, and University of Cincinnati ranked first in total citations (n = 832).
In terms of periodicals, the journal analysis can provide important information about high-impact journals.Impact factor (IF), journal citation report categories and total citations are important indicators to measure journal quality.There are nearly 40% of articles focusing on SGS published in Laryngoscope (IF = 2.6, Q3), Annals of otology rhinology and Laryngology (IF = 1.4,Q3) and International journal of pediatric otorhinolaryngology (IF = 1.5, Q4) Table 1.It showed that SGS research results were published mainly in otolaryngology, Head and Neck Surgery, Pediatric Surgery, and Thoracic Surgery.

Research focuses
The results of keyword analysis showed that "management, " "subglottic stenosis, " "tracheal stenosis, " and "laryngotracheal stenosis" were the centers of keyword clustering, and the research hotspots have gradually changed over time, from initial surgical treatment to conservative treatment.For example, early keywords that appeared more frequently were "tracheotomy, " while more recent keywords appear to be "balloon dilation."

The most influential articles
The most cited publication of SGS was "Proposed Grading System for Subglottic Stenosis Based on Endotracheal Tube Sizes" by Myer, CM et al. in 1994 [7].To harmonize the treatment rules of SGS, they proposed a simple and reproducible System for Subglottic Stenosis based on endotracheal tube sizes.They present a conversion of tube size to the proposed grading scale: grade I up to 50% obstruction, grade II from 51 to 70%, and grade Ill above 70% with any detectable lumen.An airway with no lumen is assigned to grade IV.Patients in grades 1 and 2 are usually treated non-surgically, while surgical treatment is indicated for patients in grades 3 and 4.
"Postintubation Tracheal Stenosis Treatment and results" published by Grillo, HC et al. in 1994 was the second d most-cited article [24].They found that a patient with tracheal stenosis that had failed to respond to conventional treatment recovered after antacid therapy.They constructed an experimental model of the correlation between gastric acid and airway stenosis consisting of 503 patients with tracheal stenosis.Studies have found that airway narrowing from tracheal intubation can be largely prevented by careful management of the stoma tube.
"Clinical features and therapeutic management of subglottic stenosis in patients with wegener's granulomatosis" by CA, Langford et al. in 1996 was the third most-cited article [25].They reviewed 43 cases of patients with SGS and 20 patients treated with endotracheal glucocorticoid injections to determine the clinical features and optimal treatment of subglottic stenosis (SGS) in patients with Wegener's granulomatosis (WG).Eventually, they found that SGS often occurs independently of other features of active WG and is frequently unresponsive to systemic immunosuppressive therapy.

Limitations
This study provided bibliometric information related to SGS extracted from Web of Science Core Collection database.Although this analysis was relatively comprehensive and objective, it had several limitations.First, some of influential articles that were not included in this database, so they were excluded from our study.Second, our search criteria were limited to articles in English, we might have missed out some of high-impact articles written in other languages.Third, the date of our retrieval and extraction of data was August 1st,2022.Part of the data correspond to dynamic changes, but the trend of changes will not be extensive.

Conclusion
This bibliometric analysis showed the increasing trends in published articles related to SGS over the past 10 years.The United States has contributed the most to the SGS literature.Laryngoscope, Annals of otology rhinology and laryngology and International journal of pediatric otorhinolaryngology are the top three journals with most publications.Conservative treatment has been the focus of recent research.Besides, the 100 most cited papers provide an important reference for future researchers.

Fig. 2 Fig. 1
Fig. 2 Highest impact institutions publishing on SGS.(A) The 8 institutions with the most publications.(B) The 10 institutions with the most citations.(C) Network visualization map demonstrating institutional collaborations related to SGS

Fig. 3
Fig. 3 Keyword analysis.(A) Network visualization map showing cluster analysis of keywords associated with SGS.(B) Network visualization map showing evolution of keyword frequency over time.Colors were assigned according to the average year in which keywords appeared in articles.(C) Network visualization map showing density of keywords

Fig. 4
Fig. 4 Analysis of the top 100 most-cited publications on SGS.(A) Year of publication.(B) Distribution of publications by country of origin.(C) Institutions with more than three publications

Fig. 5
Fig. 5 Keyword analysis of the top 100 most-cited publications on SGS.(A) Network visualization map showing cluster analysis of keywords associated with SGS.(B) Network visualization map showing evolution of keyword frequency over time

Table 1
Journals publishing most on subglottic stenosis

Table 2
The top 100 most-cited articles on subglottic stenosis Montgomery Surgical Management of Supraglottic and Subglottic Stenosis

Table 3
Top 5 journals publishing the 100 most-cited articles on subglottic stenosis

Table 4
Top 5 authors contributing to the 100 most-cited articles on subglottic stenosis